Clefts of the lip and palate often result in significant nasal deformities which tend to reduce the size of the nasal airway. Similarly, surgical procedures to correct nasal asymmetry, palatal incompetency or maxillary deficits can also impair nasal breathing. A significant number of clinicians have suggested that impairment of nasorespiratory function influences dentofacial growth; others disagree. The controversy stems primarily from our inability to define airway impairment quantitatively and assess mouthbreathing objectively. In cleft palate the emphasis has been on esthetics and speech with little concern for airway patency in spite of the fact that treatment can compromise the upper airway. The specific aims of this research are to use newly developed quantitative techniques to: 1. determine how the nasal airway of cleft lip/palate individuals differs from normals in terms of patency, 2. evaluate the effects of nasal surgery, palatopharyngeal surgery, maxillary osteotomies, maxillary expansion and prosthetic speech appliances on the cleft nasal airway, 3. quantify the effects of cleft lip/palate on respiratory mode i.e. ratio of nasal to oral breathing, 4. assess the effects of nasal, palatopharyngeal and maxillary surgery as well as prosthetic speech appliances on respiratory mode, 5. determine the relationship between nasal airway size and breathing mode in cleft lip/palate subjects, 6. determine whether head posture is influenced by nasal airway size and respiratory mode. Recent advances in technology provide the opportunity to quantitatively assess breathing in this special group of patients. Such information could be critical for desisions relating to physical management. One approach will be to measure nasal airway cross-sectional size using a technique developed by Warren for speech research. Its validity has been substantiated in a number of laboratories and recent studies demonstrate its usefulness for identifying airway impairment. The other technique is a simple, non-invasive method for measuring oral-nasal respiration. The methodology, involving inductance plethysmography provides an accurate way to measure respiratory mode or nasal-oral contributions to breathing in children and adults. This research represents a new direction in the objective quantification of upper airway breathing and airway impairment in the cleft population. The results are expected to provide needed information concerning the immediate and long-term effects of physical management. Additionally, these studies offer a diagnostic tool for measuring airway impairment in a new dimension, one which can readily be used for comparison as growth proceeds as well as before and after physical management.